Whisk the soy sauce, scallion, sugar, vinegar, broth, cornstarch, and chili-garlic oil in a small bowl until the sugar dissolves.

Heat a large skillet or wok over medium-high heat until the oil shimmers. Add half of the neutral oil and then the mushrooms.

Sear the mushrooms undisturbed for 2 minutes to develop a deep brown crust. Continue cooking for about 3 minutes, stirring occasionally, until they are evenly browned and have released their moisture.

Remove the mushrooms from the pan and set aside. Heat the remaining oil in the same pan over medium-high heat and add the ginger, garlic, red onion, chiles, and Szechuan pepper.

Lower the heat to medium and cook until the aromatics are fragrant and the garlic is just beginning to turn golden, about 1 minute.

Add the bell pepper and stir-fry over medium-high heat for 2 to 3 minutes until tender but still vibrant.

Return the mushrooms to the pan. Give the sauce a final stir to lift the starch from the bottom of the bowl, then pour it over the vegetables.

Toss over medium heat until the sauce thickens into a glossy glaze that clings to the mushrooms. Fold in the peanuts and season with salt.

Serve immediately while hot and glossy, topped with fresh scallions.